In the conventional CRT (Cathode Ray Tube) display device, the contour emphasizing processing is carried out aiming at high picture quality implementation and high-pass characteristic compensation. The contour emphasizing circuit to carry out this contour emphasizing processing is, as shown in FIG. 1, composed of an Y/C separation circuit 10, a color demodulation circuit 12, a contour extracting circuit, phase adjustment circuits 16, 18 and 20, an adder 22 and a matrix circuit 24.
The Y/C separation circuit 10 separates a Y (luminance) signal and a C (color) signal from the composite video signal (for example, compound color television signal) input to an input terminal 26, and the color modulation circuit 12 separates a Y signal, an R-Y (color difference) signal and a B-Y (color difference) signal on the basis of a Y signal and a C signal.
The contour extracting circuit 14 extracts a contour component Ye which is a high-pass component of a video signal on the basis of an adder 22.
The matrix circuit 24 prepares a signal adding the contour component Ye to the R (red), G (green) and B (blue) signals, respectively, on the basis of (Y+Ye) signals added by the adder 22, an (R-Y) and a (B-Y) signal phase-adjusted by phase adjustment circuits 18 and 20. That is to say, the matrix circuit 24 prepares R+Ye, G+Ye and B+Ye on the basis of the operations in following equations (1), (2) and (3). By outputting these R+Ye, G+Ye and B+Ye to the CRT display device by means of output terminals 28r, 28g and 28b, videos contour-emphasized by this CRT display device are displayed. EQU (R-Y)+(Y+Ye)=R+Ye (1) EQU (G-Y)+(Y+Ye)=G+Ye (2) EQU (B-Y)+(Y+Ye)=B+Ye (3)
(G-Y) in the above equation (2) is generated by the following equation (4).
When a video contour-emphasized by a matrix type display device driven by digital video signals (for example, R, G and B signals) like PDP and LCD is displayed, each signal of (R+Ye), (G+Ye) and (B+Ye) obtained in output terminals 28r, 28g and 28b in FIG. 1 is output to the display device after being digitized by the A/D (analog/digital) conversion circuit. However, in such a prior example, when a large amplitude signal is input to an input terminal 26, or when the contour emphasizing quantity (or contour emphasizing coefficient, the description is omitted, as it is similar afterwards) is "large", there is a problem that the correct operation cannot be obtained over the dynamic range of A/D conversion circuit.
For example, in case a large amplitude signal is input to the input terminal 26, by outputting a signal over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG. 2(a) from output terminals 28r, 28g and 28b, there are problems that signals exceeding an upper conversion reference voltage value VRT (for example, 5 volts) in the dynamic range as shown at the right-hand in said figure (a) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRT (for example, 3 volts) in the dynamic range are cut, resulting in producing black crushing.
Further, when the contour emphasizing quantity of the contour extracting circuit 14 is "large", there are problems that signals over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG. 2(b) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRB are cut, resulting in producing black crushing.
The present applicant simultaneously proposes a contour emphasizing circuit as shown in FIG. 3 as a separate application to solve the above mentioned problems.
The contour emphasizing circuit shown in FIG. 3 consists of A/D conversion circuits 30r, 30g and 30b, a signal processing/phase adjustment circuit 32, contour adders 34r, 34g and 34b, a Y signal generation circuit, a contour extracting circuit 38, a gain controller 40 for the contour component and a coefficient multiplication circuit 42.
Hence, analog R, G and B signals input to input terminals 44r, 44g and 44b are converted to digital signals by A/D conversion circuits 30r, 30g and 30b, signal-processed and phase-adjusted by the signal processing/phase adjustment circuit 32, and input to contour adders 34r, 34g and 34b. The Y signal generation circuit 36 generates Y signals from digital R, G and B signals, the contour extracting circuit 38 extracts contour components from Y signals, these extracted contour components input to contour adders 34r, 34g and 34b through the gain controller 40 and coefficient multiplication circuit 42, are added to the original digital R, G and B signals, and supplied to the display device through output terminals 86r, 86g and 86b.
As described above, it has been designed that by adding the contour components after the conversion to digital R, G and B signals by A/D conversion circuits 30r, 30g and 30b, the contour emphasizing component as a conventional example does not surpass the dynamic range of the A/D conversion circuit. For this reason, when the analog R, G and B signals input to input terminals 44r, 44g and 44b in FIG. 3 are large amplitude signals, or even when the contour emphasizing quantity is "large", neither white crushing nor black crushing is produced when outputting signals from the contour emphasizing circuit in FIG. 3 to the display device driven by digital R, G and B signals and the contour-emphasized video is expressed.
However, in the contour emphasizing circuit shown in FIG. 3, since the contour extracting circuit 38 extracts a vertical contour component on the basis of signals delayed by a specified number of lines (for example, portion of 1 or 2 lines), a Y signal generated by the Y signal generation circuit 36 and this signal, and a horizontal contour component is extracted on the basis of signals delayed by a specified number of dots (for example 2 or 4 dots), a Y signal delayed by a specified number of lines (for example, portion of 1 line) and this Y signal, as shown in FIG. 4(a) and (b), there is a problem that a processing error (for example, white edge) is produced in the periphery 11 of the display screen. FIG. 4(a) shows the case when the aspect ratio displays a video of 4:3 in a general purpose television set whose aspect ratio is 4:3, the same figure (b) shows the case wherein the aspect ratio displays a video of 4:3 in a wide television set whose aspect ratio is 16:9, and 13 indicates the side color (for example, black) without video display.
That is to say, in FIG. 4(a), the periphery 11 of the display screen corresponds to the blanking portion of the video and the boundary portion of an effective video signal, in the same figure (b), the top and bottom of the periphery 11 correspond to the blanking portion of the video and the boundary portion of the effective video signal, the right and left of periphery 11 correspond to the side color 13 and the boundary portion of the effective video signal, and since the contour extracting processing is carried out between lines or between dots without correlation to these boundary portions of effective video signal, thereby a contour emphasizing processing error comes to be produced by the interference between the insignificant signal and the significant signal.
For example, in the boundary portion of the effective video signal described above, as shown in FIG. 5(a), since the vertical display area signal VW and the vertical contour component by the Y signals corresponding to signals VW1 (display video and same phase) and VW2 which delayed a vertical display area signal VM and this vertical display area signal VW for 1 line and 2 lines are extracted, large contour components are extracted in the upper edge (portion of 1 line) 11u and lower edge (portion of 1 line) 11d of the display screen, and the contour emphasizing processing becomes excessive, resulting in deterioration of the picture quality. Besides, as shown in FIG. 5(b), since the horizontal contour components are extracted by Y signals corresponding to a signal HW1 (display video and same phase) and HW2 which delayed the horizontal display area signal HW and this horizontal display area signal HW1 in the portion of 1 line and in the portion of 2 lines, large contour components are extracted in the left-hand edge (in the portion of 2 dots) 111 and right-hand edge (in the portion of 2 dots) 11r of the display screen, the contour emphasizing processing comes to be excessive, resulting in deterioration of the picture quality.
The present invention has been carried out taking into account problems described above, when a large amplitude is inputted, or even when a contour emphasizing quantity is "large", which aims at realizing a contour emphasizing circuit that can display a contour emphasizing video without white crushing or black crushing in a display device driven by digital video signals as well as preventing the production of a contour emphasizing processing error in the display portion corresponding to the boundary portion of the effective video signal.